By JON CARAMANICA

June 2, 2014

EAST RUTHERFORD, N.J. — The last time 50 Cent appeared at Hot 97 Summer Jam, in 2004, he was the most popular rapper of the day, the most feared, and in some circles, the most hated. But what could have been a coronation was instead a fiasco: Some old enemies started trouble in the crowd, sending chairs flying toward the stage, which 50 Cent and his crew sent flying right back before walking off with a harrumph and a ban from future Summer Jams.

But if there is one lesson taught year in and year out at Summer Jam, the annual self-celebration concert thrown by Hot 97 (WQHT 97.1 FM), the city’s leading hip-hop station, it’s that anything that has been torn asunder can always be reunited.

And so there was 50 Cent, a decade later, performing late in the show Sunday night at MetLife Stadium here. And while bygones were being bygones, he shared the stage with Nas, a former foe, and reunited with the members of his old G-Unit crew — Lloyd Banks, Tony Yayo, Young Buck — all of whom he had swapped barbs with in the news media in recent years. In retrospect, that was an obvious setup for a climactic reunion, one that far outshone the new music that 50 Cent performed to an almost total lack of interest.

Declarations of war or cease-fires: Those are the great Summer Jam moments. And for years hip-hop — New York hip-hop in particular — had plenty of those on offer.

But the genre has become less tense, less overtly confrontational, and its center is nowhere near New York, which means that Summer Jam has to find new traditions, or new believers in the old ones, or accept that Summer Jam can’t be what it once was.

Which is fine, as long as it has high points like Sunday’s sometimes great show, which was often received indifferently, even at its peaks. The Los Angeles producer DJ Mustard had the thankless task of closing the show as people were streaming to the parking lot, but he persevered with an undeniable clutch of hits. His guests — the understated R&B singer Ty Dolla Sign, the wiry rapper YG and the generally blank and inexplicably popular Kid Ink — were all secondary to his beats, which throbbed with bass that literally rattled the stadium seats.

Closing the show this way was a (slightly backhanded) acknowledgment of the party rap that is at hip-hop’s commercial center, even though none of it comes from New York. Instead, the city’s current wave was represented by Action Bronson, lovable and baffling to most of the crowd; ASAP Ferg, who sprang into DJ Mustard’s set with rabid energy; Mack Wilds, on the afternoon’s festival stage program, rapping and singing as if were 1996; French Montana, sleep-rapping during Nas’s set; and Troy Ave, tepid and preoccupied with his (uncertain) place in New York’s hip-hop legacy.

Claiming the city is a perennial theme and an irrelevant one, like wearing the jersey of an old championship team. It shows you know your history, but maybe not what’s happening right next door.

But New York is Hot 97’s business, and so in the absence of a genuine new guard, it trotted out the old one. 50 Cent is a charter member, as is Nas, who performed songs from his 20-year-old classic album, “Illmatic,” numbers so old he used a teleprompter to remember the lyrics. Fabolous had a moment of shine during 50 Cent’s set, and the local ruffian heroes the Lox and M.O.P. performed with the Roots (probably the first time either was backed by a tuba). But there was no Jay-Z, no Diplomats, no Diddy, no Wu-Tang Clan — none of the old firebrand titans.

They don’t make titans like they used to, from any town. Some here tried to argue their case, though: Meek Mill, who Nas regarded almost lovingly as he screamed a few of his hits. (Not much is ever said about the humility it requires to let someone outright steal your set out from under you — kudos to Nas for playing along.); Wiz Khalifa, whose impressive, loose performance verged on punk rock and featured a slick Snoop Dogg; and artists chosen to appeal to specific constituencies, including thirsty women (the loverman R&B singer Trey Songz), thirsty men (the rising R&B singer Sevyn Streeter) and Caribbean fans (the regal soca star Bunji Garlin).

Would-bes, all of them. The only real royalty came late in the night, during the circle-closing performance of Nicki Minaj. Two years ago, set to headline Summer Jam, she walked out in response to some unkind words by Peter Rosenberg, one of the station’s D.J.’s, about her pop inclinations. She made a brief token appearance last year, but this was her proper comeback. (Never mind the paradox that one of the performers at the afternoon show was an even more obvious outlier, Iggy Azalea, the white Australian female rapper who appears on the No. 1 and 2 pop songs on the current Billboard Hot 100. On this matter, Mr. Rosenberg was silent, though he gamely flirted with Ms. Azalea on a recent episode of Hot 97’s VH1 comedy show, “This Is Hot 97.”)

Ms. Minaj did not perform “Starships,” the song Mr. Rosenberg maligned — that would have been pointed and fun, but not in keeping with the reconciliation. Instead, she relied on her strengths. She was magnetic and lyrically fierce, the only real star of the night, apart from the Young Money label mates she brought out with her, Lil Wayne and Drake.

Young Money is a family with its own internal strife, though not as public as G-Unit’s, and Ms. Minaj jokingly expressed disappointment with Drake before he came out on stage. They both rooted heartily for Lil Wayne, himself in the midst of a minor comeback. Ms. Minaj also graciously gave stage time to a younger guard — Young Thug and Soulja Boy from Atlanta, Lil Herb from Chicago — with whom she has collaborated lately, solidifying her as the most open-eared major hip-hop star of the day, not just one of the most talented.

Ms. Minaj is from Queens, but that she’s a local hero hardly mattered during her unity-themed set. Summer Jam is no longer the register of hometown alliances and squabbles, but an open-door event for out-of-town friends — a former exporting nation getting acclimated to living off imports.

Except for one tiny little thing. It turns out 50 Cent wasn’t totally in a healing mood — he’s not quite a rap star these days, but was clearly relishing sipping from the old elixir. During his set, a scuffle erupted behind him: A rapper from the group Slow Bucks was assaulted and robbed of his chain. Reports suggest that 50 Cent, who has beefed with that group in the past, then put on the chain; either way, he kept performing, surrounded by bodyguards, with a huge grin on his face. “Just the way I like it — it’s nice and ghetto,” he said. It was a taste of the Summer Jams of old, and maybe grist for Summer Jam 2024.